Question

question and answer of acid bases and salt cbse class 7ex

Answer 1

 State the differences between acids and bases.

Ans.)

Acids   Bases

a) Taste of acids is sour. a) Taste of bases is bitter.b) Acids turn blue litmus paper into red. b) Bases turn red litmus paper to blue.c) Acids contain H+ ( hydrogen ion) c) bases contain OH- ( hydroxyl ion)

 

Q -2) Ammonia is found in many household products, such as window cleaners. It turns red litmus paper blue. What is its nature?

Ans.) Ammonia is having a basic nature.

 

Q-3) Name the source from which litmus solution is obtained. What is the use of this solution?

Ans.) Litmus solution is extracted from lichens and is used to determine whether the given solution is basic or acidic.

 

Q-4) Is distilled water acidic or basic or neutral? How would you verify it?

Ans.) Distilled water is neutral. One can verify it by showing that neither red nor blue litmus paper changes its colour when dipped in distilled water.

 

Q-5) Describe the process of neutralization with the help of an example.

Ans.) The reaction which occurs between acid and base is known as neutralization. Salt and water are by-products in this process and heat is also liberated.

Magnesium hydroxide, baking soda, etc. which contain bases are used to reduce acidity in our stomach.

Q-6) Mark “t” if the statement is true and “f” if it is false:

a) Nitric acid turns red litmus paper into blue. (t/f)b) Sodium hydroxide and hydrochloric acid neutralise each other and form water and salt. (t/f)c) Sodium hydroxide turns blue litmus paper into red. (t/f)d) Tooth decay is caused by the presence of a base. (t/f)e) Indicator is a substance which shows different colours in basic and acidic solution.

Ans.) (a) f (b) t (c) f (d) f (e) t

 

Q-7) Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are not labelled. He has to serve the drinks on the demand of the customers. One customer wants an acidic drink, another wants a basic and third one wants a neutral drink. How will Dorji decide which drink is to be served to whom?

 

Ans.) Dorji can decide this with the help of a litmus paper

a) If blue litmus turns into red when dipped in the drink, then the drink is acidic.b) If red litmus turns into blue when dipped in the drink, then the drink is basic.c) If the colour of litmus paper does not change when dipped in the drink, then the drink is neutral.

 

Q-8) Explain why:

1)         An antacid tablet is taken when you suffer from acidity.

2)         Factory waste is neutralised before disposing it into the water bodies.

3)         Calamine solution is applied on the skin when an ant bites.

Ans.)

1) We take an antacid like magnesium hydroxide to neutralise the extra acid which is released in our stomach.

2) The waste which comes from factories contains acid, and if this acid is dumped into the water body, it harms the organisms present in it. So it is necessary to neutralise this waste by adding a basic substance.

3) Ant injects Formic acid (an acidic liquid) into the skin by biting our skin which causes inflammation of the skin. The effect of the acid can be neutralised by rubbing the skin with Calamine solution which contains a weak base like zinc carbonate so that it causes no harm to the skin.

 

Q-9) Three liquids are given. One is hydrochloric acid, another is sugar solution and third is sodium hydroxide. How will you identify them? You have only a turmeric indicator.

Ans.)

Name   Effect on turmeric indicator

Hydrochloric acid       Yellow to blue

Sugar Solution            No change

Sodium Hydroxide     Yellow to red

 

Q-10) Blue Litmus paper is dipped in a solution. It remains blue. What can be said about the nature of the solution? Explain.

Ans.)

a) When litmus paper is dipped into a basic solution, it turns blue. Here, as the colour of the litmus paper is not changed or affected, the given solution is basic in nature.

b) Even when the solution is neutral, the colour of the litmus paper will not change.

 

Q-11) Consider the following statements:

i) Both acids and bases change colour of all indicators.

ii) If an indicator gives colour change with a base, it doesn’t change colour with an acid.

iii)        If an indicator changes colour with an acid, it doesn’t change colour with a base.

iv) Change of colour in an acid and a base depends on the type of the indicator. Which of these statements are correct?

a) All four           b) (i) and (iv)           c) (ii) and (iii)           d) only (iv)

 

Ans.) b) (i) and (iv)